Dyeing polyester sutures with indigo and the coating of the dyed sutures



3,527,556 Patented Sept. 8., 1970 3,527,556 DYEING POLYESTER SUTURESWITH INDIGO AND THE COATING OF THE DYED SUTURES Herbert Joseph Riley,New Milford, Conn., assignor to American Cyanamid Company, Stamford,Conn., a corporation of Maine No Drawing. Filed Dec. 8, 1966, Ser. No.600,029 Int. Cl. D06p /16 US. Cl. 8--17 4 Claims ABSTRACT OF THEDISCLOSURE Surgical sutures of poly (glycol terephthalate) are dyed withnatural or synthetic indigo, at about the boil, in an aqueous bathbetween about pH 4 and6 in the presence of sufficient sodium ion andsodium hydrosulfite to transform the indigo into the yellow sodium leucoform, followed by oxidizing the indigo to its blue form. Releucoing andsilicone coating may be used.

This invention relates to sutures of poly (glycol terephthalate) dyedwith indigo.

Sutures of poly (glycol terephthalate) will be referred to throughoutthe rest of this specification by the registered trademark Dacron, usedby the Du Pont Company for their polyester fiber. This is a typical poly(glycol terephthalate) fiber, but the invention is not limited to theuse of fibers from this source. These sutures have 0 many advantages,including high tensile strength, inertness to tissue, and the like. TheDacron fiber, as purchased, is white or colorless, and there has been ademand for colored sutures. It has been proposed to dye Dacon sutures bymeans of oil soluble dyes in an organic solvent, such as dimethylformamide. This is described in US. Pat. 2,909,177. The presentinvention is directed to a process of dyeing Dacron sutures with the vatdye, indigo, natural or synthetic, from baths which do not containorganic liquids and hence do not tend to dissolve or soften the Dacron.

Vat dyes, such as indigo, have many valuable characteristics, notablyextreme fastness, inertness, non-toxic ity, and the like. However, ithas been found that ordinary vat dyeing techniques are not satisfactoryfor dying sutures of Dacron with indigo. Several requirements arenecessary. First of all, the dyeing procedure must not injure the Dacronsuture by reducing its tensile strength or knot strength. Secondly, thedyed suture must not crock or bleed when in contact with tissue ortissue fluids. Thirdly, it is very desirable that the dyeing be uniform.

Dacron sutures must not have high capillarity, or at least thecapillarity must be rigidly controlled so that excessive absorption offluids from body tissues will not take place. This prevents transfer ofinfection. A preferred method for doing this is by coating the suturewith a thin coating of silicon rubber. The use of silicone coating fornon-absorbable sutures is described in US. Pat. 3,187,752.

It has been found that a coating of silicone rubber not only reduces thecapillarity of the suture, but it also improves its handling propertiesand knot tieing characteristics. Sometimes sutures are used in deeprecesses of the body to approximate tissues or to ligate blood vessels.When they are used in deep recesses longer sutures are required thanwhen they are used near the surface. If, for example, a deep lying bloodvessel is to be ligated, the center portion of the suture is loopedaround the vessel and the knot is started at the remote ends of thesuture. The suture ends are drawn apart to move the knot down to thevessel. As one suture strand is pulled over the other until the knot isset abrasive action results which can cause the knot to chatter duringrun-down or the suture to fray.

Silicon coating of sutures minimizes or eliminates chattering orfraying. The coating allows the strands to glide over each other and atthe same time offers protection against abrasion.

No problem is presented with white Dacron sutures which can be handledin the same manner as other materials, such as for example silk;however, in the present invention, as will be brought out below, aserious problem arises if the ordinary silicone treatment is carried outunder the conditions which are standard for other materials and forwhite Dacron sutures. Ordinarily, silicone rubber contains a smallamount of a peroxide catalyst, such as benzoyl peroxide, which is usedto effect the initial polymerization of the silicone to producecommercial solutions of satisfactory viscosity.

When non-absorbable sutures such as silk or white Dacron art coated witha silicone rubber, it is standard procedure to increase theconcentration of the peroxide catalyst so that the coating cures morerapidly and has greater resiliency. However, too high a concentration ofperoxide catalyst reacts adversely with the indigo producing a dull,unlevel greenish-blue color instead of full deep, level shades of bluethat are desired. Therefore, in

, addition to the requirements for the dyeing step itself,

there are certain critical limitations on catalyst content in thesilicone rubber treatment step of the suture.

Indigo has been dyed on cellulosic materials by two different generalmethods: One, a highly alkaline method in which high alkalinity isobtained with sodium hydroxide and the dyeing is from the sodium leucoof the vat dyestuff, which is yellow in color; two, dyeing at loweralkalinities (pH values less than 7) in which the indigo is reduced toits white hydrogen leuco, sometimes referred to as vat acid. Neither ofthese procedures is useful for dyeing sutures of Dacron. The firstprocedure, while capable of producing a good blue color, adverselyaffects the chtaracteristics of the suture, such as tensile strength andthe like. The second process does not adversely affect the properties ofthe suture, but neither does it dye it. There has, therefore, been aneed for a process of dyeing the sutures with the yellow sodium leucounder conditions which do not injure the suture and which include dyeingon the slightly acid side, for example near a pH of 5, which iscomparable to the pH for vat acid dyeing. The effectiveness of thedyeing, however, requires certain very definite conditions.

For best results, the dyeing must be at high temperatures, preferably atthe boiling point of water. It is believed that the penetration of thesodium leuco into the Dacron suture is a thermally influence-d process.A second factor is that there must be in the vat sufficient sodium ionso that the sodium leuco of the indigo is formed. This is entirely apartfrom the pH at which the dyeing takes place, because this latter isdetermined by a balance of the reducing agent, sodium dithionite, Na S Owhich will be referred to throughout the specification by the commondesignation in the art of hydrosulfite, and whatever alkali is present.In other words, at the same pH the indigo might be present as itshydrogen leuco or as its sodium leuco, depending on the sodium ionconcentration, and the latter is an essential feature of the presentinvention.

It has been found necessary to take care that the sutures are completelysubmerged in the dye bath until the penetration by the sodium leuco iscomplete. This requirement necessitates maintaining the dye bath volumeregardless of the actual weight of sutures being dyed, which is quite adifferent situation than that in ordinary vat dyeing where chemicalamounts are based on the weight of the material being dyed. Usually whencarrying out the process of the present invention the sutures are dyedin skein form, care being taken to tie the skeins sufficiently looselyso that the individual sutures are contacted adequately by the dye bathon all sides during the dyeing. It is also possible to dye by packagedyeing procedures, but care must be taken that the packages besufficiently loosely wound so that imperfect dyeing at the point wherethe material crosses in the package is not encountered. This problem,which is usually referred to in the art as the cross-over problem issomewhat more severe with Dacron sutures than with the vat dyeing ofother materials, such as for example cotton yarn, which is more porousand can absorb the dye bath effectively. The Dacron sutures, of course,are not porous as far as the individual filaments are concerned and sosomewhat greater care must be exercised if the present invention isconducted in a packaged dyeing procedure. While greater care isnecessary, it is well within ordinary dyeing skill, and therefore theprocess of the present invention can be carried out using package dyeingtechniques.

The problem of peroxide catalysts concentration in the silicone coatingstep, which has been referred to above, is a concentration problem, andin general in the present invention the peroxide catalyst, such asbenzoyl peroxide, should not be present in concentrations whichsubstantially exceed about 3%. As the commercial silicone rubber usuallycontains about 2% to 2.5% of benzoyl peroxide, it is normally desirableto effect the silicone coating step without any added benzoyl peroxide,and this is the preferred procedure. However, if the benzoyl peroxidecontent of a particular batch of silicone rubber is unusually low, it ispermissible to add small amounts of benzoyl peroxide, care being takenthat the amounts added do not produce a concentration substantially inexcess of 3%. If this concentration is substantially exceeded, the colorof the dyed suture becomes greenish blue and of low color intensity andsuch sutures are less visible in the presence of blood and do not showup well in contrast to tissue.

The dyeing procedure utilizes a well known step to avoid crocking and toproduce deep colors. Thus, when the Dacron sutures are first dyed with asodium leuco and the color developed by oxidation, there may beinsufiicient penetration of the dye into the Dacron fibers and it is acommon procedure in the dyeing art to again reduce, the so-calledreleuco procedure, and then again oxidize. Full, deep shades of blue areproduced which have not been practical hitherto with indigo. Crocking isalso reduced and, of course, the silicone coating which follows alsohelps to prevent any undesired crocking.

The invention will be described in greater detail in conjunction withthe following specific example, in which the parts are by weight unlessotherwise specified. The example is a typical one and uses typicalequipment, but

this invention is not limited to the exact details therein set forth solong as the process requirements which have been set out above are met.

EXAMPLE A steam heated, stainless steel tank is used which can handle 90gallons of bath (747 lbs, of water). Up to 21 lbs. of Dacron sutures canbe dyed at one time, and all quantities of chemicals set out below areexpressed as a percentage of the weight of water instead of a percentageof the weight of the fiber dyed, as in most conventional dyeingprocedures. Skeins of braided Dacron sutures are supported by astainless steel rack which holds the skeined Dacron submerged during thedyeing procedure; the skeins should be sufficiently loosely tied topermit the dye bath to attack all sides of the braided sutures.

The skeined Dacron is scoured with 0.5% detergent (40% flake-sodiumlinear alkylaryl sulfonate) flakes, for 30 minutes at the boil. A smallamount of anti-foaming agent emulsion of dimethyl poly siloxane) isadded to prevent the bath from boiling over. The bath is then drainedfrom the tank and 90 gallons of cold water added, the temperature israised to 70-80 C., and the sutures rinsed in this hot water bath for 10minutes, followed by draining, as set out above, and raising the skeinsout of the bath.

The rinse bath is drained and 90 gallons of cold water added. 49 gramsof D&C Blue #6 (indigo) is pasted with a dispersing agent (sulfatedfatty acid) and then is added to the cold water in the dye tank, thebath is stirred until a uniform dispersion is obtained, a small amountof antifoaming agent is added, and the temperature of the dye bath thenraised to about 70 C. 0.35% sodium hydrosulfite is added, the bath beingmaintained between 70 and C. the above noted D&C Blue #6 is C.I. VatBlue 1 having Colour Index No. 7300, reference; Colour Index, 2ndEdition, 1956, vol. 4, page 4217, published by The Society of Dyers andColourists, Yorkshire, England.

Technical grade sodium hydrosulfite Na S O is used. Care must be takento protect the hydrosulfite in storage from moisture and fromatmospheric oxidation. If the salt is excessively exposed it willdeteriorate. Loss in potency of the hydrosulfite will require additionalamounts than those indicated to be added during the dyeing cycle.

The tank is covered, and after a short wait 0.014% of sodium hydroxideis added, followed, after a short wait, with an additional 0.57% ofsodium hydrosulfite and then a second like amount. The temperature ofthe bath is then raised to 100 C. and the skeined Dacron lowered intothe boiling dye bath. The tank should be covered to prevent surfaceoxidation. At this point the dye bath is yellow, which is the color ofthe sodium leuco of indigo. A 250 ml. sample of the dye bath is thenremoved and the pH is taken at about a temperature of 70 C. The pHshould be between 5 and 5.5 when measured on a Macbeth pH Meter Model1051 using a glass electrode. If the color of the dye bath is not yellowat this step, allow the temperature of the bath to drop to 98 C. Add anadditional 0.57% sodium hydrosulfite to the dye 'bath and raise thetemperature to the boil. This step may be necessary if the sodiumhydrosulfite has lost potency. The Dacron skeins are boiled for about 15minutes, raised above the tank and rotated, then lowered again andboiled for an additional 15 minutes. The skeins are raised again and,the dye bath is then drained from the tank, which is refilled with 90gallons of cold water, 1.25% of sodium per-borate, technical grade, and0.014% glacial acetic acid are stirred in, and the temperature raised to70-80 C. A small amount of anti-foaming agent is then added. The bath israised to the boil and the Dacron skeins are directly introduced intothe oxidizing bath at the boil. After 15 minutes the skeins are raised,moved on the rack to straighten out any crooked skeins, and againlowered and boiled for 15 minutes. The skeins are then raised, the tankdrained, refilled with water, the temperature raised to 70-80 C., andthe skeins returned and rinsed in the hot water.

After rinsing, the skeins are raised, the tank is again drained andrefilled with cold water and heated up and 0.5% of soap flakes addedwith a small amount of antifoaming agent. The skeins are re-introduced,the bath heated up to C. and boiled for 15 minutes. After 15 minutes theskeins are raised, moved on the rack to straighten out any crookedskeins, and again lowered and boiled for 15 minutes. The tank is againdrained and refilled with cold water. The water is heated up and the hotwater rinse, as described above is repeated.

The dyed skeins are then releucoed by repeating the treatment withsodium hydrosulfite and sodium hydroxide described above. If the colorof the skeins is not bluish green at this step, allow the temperature ofthe bath to drop to 95-98" C. and add an additional 0.57% sodiumhydrosulfite to the releuco bath and raise the temperature to the boil.Again, this step may be necessary be cause the hydrosulfite has lostpotency. The bath is then drained, refilled with cold water, and theoxidizing step reepated, followed by a second soaping and boiling inwater. The dyed Dacron sutures are then dried in an oven at 100-110 C.

The dyed Dacron sutures are coated with silicone rubber by preparing acoating bath of the silicone rubber and xylene containing from 2% to2.5% benzoyl peroxide, adjusting the viscosity with xylene to 5 secondsat 23 C. on a Ford fixed orifice viscometer cup having a orifice. TheDacron sutures are wound on spools or cops on a coating machine anddrawn through a reservoir and then through a suitable wiper to wipe oifexcess silicone rubber. The coated strands are then passed through threecuring ovens in series, the first one being maintained at 100 C., thesecond at 130 C., and the third at 165 0.; each oven is 36" long. Thestrands are kept taut while passing through the curing ovens to preventcontact with the oven sides. Coating speed will vary somewhat with thesize of the suture, for example 12/ min. for the size group 6/0-2/0 and97min. for the size group 0-2.

I claim:

1. A process of dyeing poly (glycol terephthalate) sutures whichcomprises,

(a) dyeing the sutures, substantially at the boil in a dye bathcontaining indigo and sufficient sodium ion and sodium hydrosulfite totransform the indigo into the yellow sodium leuco and maintain a pHbetween 4 and 6, and

(b) oxidizing to the blue colored form,

2. A process according to claim 1 in which the dyeing of suturesproceeds in the following steps:

(a) treating the sutures at the boil with the sodium leuco of indigo,

(b) oxidizing (c) soaping (d) releucoing l (e) reoxidizing (f) resoaping3. The process of claim 1 comprising the additional step of coating thedyed sutures with silicone rubber in the presence of an amount ofperoxide catalyst not substantially exceeding 3%.

4. The process of claim 2 comprising the additional step of coating thedyed sutures with silicone rubber in the presence of an amount ofperoxide catalyst not substantially exceeding 3%.

References Cited UNITED STATES PATENTS 2,774,647 12/1956 Mecco et a1.8-34 2,909,177 10/1959 DoWd et a1. 128335.5 3,187,752 6/1965 Glick117-141 X GEORGE F. LESMES, Primary Examiner T. J. HERBERT, JR.,Assistant Examiner US. Cl. X.R.

